Method and apparatus for improved reliability and reduced power in a processor by automatic voltage control during processor idle states

ABSTRACT

A method and apparatus automatically transferring to an enhanced low-power state of a processor is disclosed. In one embodiment, either all or a portion of a processor core clock distribution grid may be powered down in these enhanced low-power states. In one embodiment, the processor may operate in a reduced power supply voltage and operate at a reduced frequency during these enhanced low-power states. In one embodiment, a portion of the clock distribution grid may be left on to support snoop operations at a reduced frequency.

FIELD

[0001] The present disclosure relates generally to microprocessor systems, and more specifically to microprocessor systems capable of operating in low-power or reduced power states.

BACKGROUND

[0002] In order to conserve energy and reduce thermal load, many processors include the option of operating in several operating states. During the times when the processor is operating, the greatest processor clock frequency that is available may be selected to enhance processor throughput. However, during the times when instructions are not being processed, the processor may transfer to one of several available low-power states. In these states, the processor clock frequency may be reduced or completely stopped, but cache-coherency snooping may be permitted. In other states, enough of the processor may be powered-down that cache-coherency snooping may not be permitted, and the operating system software must provide for cache coherency. In the Pentium® class processors produced by Intel® Corporation, the normal operation state may be called the CO state, the low-power states may be called the C1, C2, C3, and C4 states.

[0003] The existing low-power C1 and C2 states are not optimal with regards power conservation. The C3 and C4 states achieve higher levels of power conservation, but have several drawbacks that limit their use. One is the inability to participate in cache-coherency snoop operations. This could mean that they cannot be used when certain “bus mastering” peripherals are attached. Such bus mastering peripherals using such connections as universal serial bus (USB) and other quick-connection interfaces are becoming increasing common. Another problem is that the low-power states may have long exit latencies (the time required to come out of the low-power states). Therefore none of these existing low-power are optimal for future processor products.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

[0005]FIG. 1 is a state diagram of processor low-power states, according to one embodiment.

[0006]FIG. 2 is a system diagram of a processor system, according to one embodiment.

[0007]FIG. 3A is diagram of an operating point register, according to one embodiment of the present disclosure.

[0008]FIG. 3B is diagram of a configuration register, according to one embodiment of the present disclosure.

[0009]FIG. 4 is a logic diagram of the selection of a frequency and voltage value, according to one embodiment of the present disclosure.

[0010]FIG. 5A is a timing diagram of turning a clock grid off, according to one embodiment of the present disclosure.

[0011]FIG. 5B is a timing diagram of turning a clock grid on, according to one embodiment of the present disclosure.

[0012]FIG. 6 is a diagram of a break event handler, according to one embodiment of the present disclosure.

[0013]FIG. 7 is a schematic diagram of a multi-processor system, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0014] The following description describes techniques for operating a processor in various extended low-power states. In the following description, numerous specific details such as logic implementations, software module allocation, bus signaling techniques, and details of operation are set forth in order to provide a more thorough understanding of the present invention. It will be appreciated, however, by one skilled in the art that the invention may be practiced without such specific details. In other instances, control structures, gate level circuits and full software instruction sequences have not been shown in detail in order not to obscure the invention. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation. The invention is disclosed in the form of a microprocessor module with an extended halt state and an extended stop-grant state. However, the invention may be practiced in other forms of processors, such as digital signal processors.

[0015] Referring now to FIG. 1, a state diagram of processor low-power states is shown, according to one embodiment. In one embodiment, a processor may operate in a normal operation state (or C0 state) 10 when actively processing instructions. In the normal operation state, the processor may be operating under conditions of supply voltage V₀ and processor core clock frequency F₀. During other operational situations, there may be many other combinations of supply voltage and processor core clock frequency Vi, Fi.

[0016] In order to conserve power, reduce thermal load, and in some cases extend reliability by reducing the voltage across gate insulation layers, the processor may transfer to a low-power state 120 whenever the processor is able. The low-power state 120 may be one of several such states well-known in the art. For example, low-power state 120 may be a halt state (or C1 state), wherein the halt state may be entered by software executing a special HALT or MWAIT instruction. During operation in halt state, large portions of the circuitry of the processor may be powered-down. Many of the processor clock circuits may be powered-down, although the distribution clock grid of the processor may be left powered-on. During the halt state, the supply voltage V₀ does not change: neither does the assigned processor core clock frequency F₀.

[0017] In addition to the halt state, the low-power state 120 may be a stop grant state (or C2 state). The stop grant state may be somewhat different than the halt state. For example, the stop grant state may be entered upon hardware in the processor receiving a stop clock STPCLK signal, which may originate in a chipset after an advanced configuration and power interface (ACPI) register is read. During operation in stop grant state, large portions of the circuitry of the processor may be powered-down. Many of the processor clock circuits may be powered-down, although the distribution clock grid of the processor may be left powered-on. During the halt state, the supply voltage V₀ does not change: neither does the assigned processor core clock frequency F₀.

[0018] When a processor is operating in a multi-processor system, it may need to cooperate in cache-coherency schemes by responding to snoop requests. If the processor is operating in a low-power state 120, such as the halt state or the stop grant state, the processor clock and cache circuits may be powered-down when a snoop request is received. Therefore a low-power state 120 may transfer to an existing (or “old”) snoop state 140, where enough of the circuits and clocks are powered-on to respond to the cache-coherency snoop request. After the request is serviced, the existing snoop state 140 may transfer back to the low-power state 120.

[0019] In order to enhance the power conservation and improve reliability provided by low-power state 120, in one embodiment an enhanced low-power state 130 may be used. Unlike the low-power state 120, no external stimuli are required to enter the enhanced low-power state 130. If the processor is operating in the low-power state 120, then when the enhanced low-power state 130 is enabled the processor automatically transfers from low-power state 120 to enhanced low-power state 130. When transferring in from a halt state (C1), the enhanced low-power state 130 may be called a C1E state. When transferring in from a stop grant state (C2), the enhanced low-power state 130 may be called a C2E state.

[0020] When the processor enters an enhanced low-power state 130, it may select one of many combinations of supply voltage and processor core clock frequency Vi, Fi different from the normal operation state 110 combination V₀, F₀. In one embodiment, the frequency F_(L), corresponding to the lowest permitted ratio of bus clock frequency to processor core clock frequency, is paired with the lowest voltage V_(L)compatible with F_(L). In one embodiment, the lowest permitted ratio is 16:1. This combination F_(L), V_(L) may then be used by an enhanced low-power state 130.

[0021] In an enhanced low-power state 130, the distribution clock grid of the processor may in some embodiments be turned off, as well as many of the clocks of the processor. The processor core phase-locked loop (PLL) which may serve as a clock reference may in some embodiments be left powered on in order to reduce the time required to synchronize clocks when leaving the enhanced low-power state 130. In such embodiments, there may be an alternate feedback path for the processor core PLL to permit locking when certain circuit elements are powered off.

[0022] In some embodiments, the distribution clock grid of the processor may be subdivided to create a processor bus interface domain as a subset of the overall clock grid. In some embodiments, a processor bus interface domain may be an input/output clock domain, which may be considered the distribution clock grid subset for the buffers and signals available at the boundaries of the processor. In other embodiments, the processor bus interface domain may be a clock domain of the sections of the processor that need to be on to monitor the internal and external break events, or may be a clock domain of the sections of the processor that need to be on to service cache-coherency snooping. In these embodiments, the enhanced low-power states may turn the power off to the distribution clock grid of the processor with the exception of the processor bus interface domain. This may permit the processor to act upon interrupts, signals on the system bus, and other interface signals. In one embodiment, the processor may support an enhanced snoop state 150. In enhanced snoop state 150, the snoop request may be serviced with the processor in operating in the supply voltage and frequency combination F_(L), V_(L). The snoop request may be adequately serviced at F_(L), V_(L) as the snoop request servicing is not processor computationally intensive. In some embodiments, the enhanced low-power state may need to transfer to the old snoop state 140 via the low-power state 120 in order to service snoop requests.

[0023] Referring now to FIG. 2, a system diagram of a processor system 200 is shown, according to one embodiment. In the FIG. 2 embodiment, processor 210 is shown connected with chipset 220 via a bus 230. The FIG. 2 embodiment may be a uniprocessor system, or there may be other processors (not shown) connected via bus 230. Chipset 220 may be a single integrated circuit, or may have its functional elements distributed among 2 or more integrated circuits. Chipset 220 is shown including an advanced configuration and power interface (ACPI) register 222. When processor 210 reads from a location in ACPI register 222, the chipset may respond with a stop clock STPCLK signal 224 to processor 210, putting processor into a stop grant (C2) state. Processor 210 also may send signals on a voltage identifier (VID) signal line 214 to a voltage regulation module 240 that supplies power to the processor 210 and possibly to other circuit elements. The signals presented by processor 210 on the VID signal line 214 may configure the power supply voltage on power line 242 supplied to the processor 210.

[0024] Processor 210 may in one embodiment include an enhanced state policy logic 212 that may contain logic elements that support the automatic transfer of the processor 210 from a low-power state 120 to a corresponding enhanced low-power state 130, as discussed above in connection with FIG. 1. Enhanced state policy logic 212 may in one embodiment turn off clock circuits within processor 210, but may permit a core PLL to continue in operation via an alternate feedback path. Enhanced state policy logic 212 may in one embodiment turn off the clock grid for the processor 210. In other embodiments, processor 210 may have the clock grid subdivided to create a processor bus interface domain 216 that supports processor 210 interface circuits such as VID signal line 214, the STPCLK signal line 224, and bus 230. In this embodiment, the enhanced state policy logic 212 may turn off portions of the clock grid other than processor bus interface domain 216 while leaving the processor bus interface domain 216 powered on. The processor 210 may respond to cache-coherency snoop requests initiated by a bus priority (BPRI) signal 226 by transferring to an enhanced snoop state 150. In embodiments without a processor bus interface domain 216, the processor 210 may respond to cache-coherency snoop requests initiated by a bus priority (BPRI) signal 226 by transferring to an old snoop state 140 via the low-power state 120. This may require not powering down the processor clock grid.

[0025] In some embodiments, enhanced state policy logic 212 may reduce the processor 210 operating voltage within an enhanced low-power state by signaling the voltage regulation module 240 via the VID signal lines 214. The enhanced state policy logic 212 may also reduce the processor core clock frequency. In one embodiment, the frequency F_(L), corresponding to the lowest permitted ratio of bus clock frequency to processor core clock frequency, is paired with the lowest voltage V_(L)compatible with F_(L). In one embodiment, the lowest permitted ratio is 16:1. This combination F_(L), V_(L) may then be set by the enhanced state policy logic 212 during the automatic transfer from a low-power state 120 to a corresponding enhanced low-power state 130. In one embodiment, the transfer to the lower processor core clock frequency occurs somewhat before the transfer to the lower voltage.

[0026] Referring now to FIG. 3A, a diagram of an operating point register is shown, according to one embodiment of the present disclosure. When a processor 210 has the enhanced low-power states enabled, which may be an enhanced halt state (C1E) or an enhanced stop grant state (C2E), the reduced supply voltage and frequency may be set by using an operating point register, which may be one of several model specific registers (MSRs) of the processor. In one embodiment, the ratio of bus clock frequency to processor core clock frequency may be set by the bits located at bits 9 through 15 in the operating point register. Similarly, the VID signal bits for the VID signal line 214 may be set by the bits located at bits 0 through 7 in the operating point register. At reset, bits 0 through 7 may be initialized with a value predetermined by the processor. In other embodiments, these operating points may be set in other ways, including being set by the system basic input/output system (BIOS).

[0027] Referring now to FIG. 3B, a diagram of a configuration register is shown, according to one embodiment of the present disclosure. The configuration register may be another MSR. In one embodiment, bit 25 may be set to enable the enhanced halt state (C1E) automatically being entered upon halt state (C1) entry. In one embodiment, bit 27 may be set to enable the enhanced stop grant state (C2E) automatically being entered upon stop grant state (C2) entry.

[0028] Referring now to FIG. 4, a logic diagram of the selection of a frequency and voltage value is shown, according to one embodiment of the present disclosure. In the FIG. 4 embodiment, there may be three registers containing a normal operation frequency and voltage value (Gv3 F/V) register 410, a thermal monitor 2 frequency and voltage value (TM2 F/V) register 412, and an enhanced low-power state (C1E C2E F/V) register 414. The values for the enhanced low-power state (C1E C2E F/V) register 414 may be as set in the operating point register of FIG. 3A. The values of the three registers may be selected by a frequency and voltage selection multiplexor 418 on the basis of a thermal monitor 2 sensor trip logic 416 and a HALT/MWAIT or STPCLK assertion logic 420. Multiplexor 418 generally passes to the goal frequency and voltage register 422 the value from the normal operation frequency and voltage value (Gv3 F/V) register 410, unless either thermal monitor 2 sensor trip logic 416 and a HALT/MWAIT or STPCLK assertion logic 420 override it. In that case, if thermal monitor 2 sensor trip logic 416 is asserted, then the value from the thermal monitor 2 frequency and voltage value (TM2 F/V) register 412 is passed to the goal frequency and voltage register 422. If the HALT/MWAIT or STPCLK assertion logic 420 is asserted, then the value from the enhanced low-power state (C1E C2E F/V) register 414 is passed to the goal frequency and voltage register 422. In case both the thermal monitor two sensor trip logic 416 and the HALT/MWAIT or STPCLK assertion logic 420 are asserted, the thermal monitor two takes priority and the value from the thermal monitor two frequency and voltage value (TM2 F/V) register 412 is passed to the goal frequency and voltage register 422.

[0029] If the comparator 426 determines that the value in the goal frequency and voltage register matches the value in the actual frequency and voltage register 424, then no action is needed. However, if they do not match, then a action is initiated in ratio change request logic 428 which initiates a new central processor power down (CPD) entry utilizing CPD_ENTRY logic 430.

[0030] Referring now to FIG. 5A, a timing diagram of turning a clock grid off is shown, according to one embodiment of the present disclosure. In one embodiment, the clock grid shut down is initiated by a bus priority (BPRI#) going inactive (logic high) during bus clock cycle 1. This may be in response to a cache-coherency snoop request having completed. Then in bus clock cycle 2 a shutdown signal is sent to grid signal point of distribution (POD) and PLL is initiated. After a distribution delay, the shutdown signal reaches the POD and PLL, and the clock at the PLL ceases operation. The clock from the PLL ceases at other points during bus clock cycle 3 due to distribution delay.

[0031] Referring now to FIG. 5B, a timing diagram of turning a clock grid on is shown, according to one embodiment of the present disclosure. In one embodiment, the clock grid shut down is initiated by a bus priority (BPRI#) going active (logic low) during bus clock cycle 1. This may be in response to a cache-coherency snoop request initiation. A wakeup signal is sent to the grid POD and PLL, which arrives at the grid POD and PLL after a distribution delay. The PLL clock begins operation a short time later, and arrives at the external bus clock (EBC) circuit. During bus clock cycle 3, the EBC circuit is synchronized, and then the ratio of bus clock to processor core clock is set during bus clock cycle 4. Then the processor may act upon bus data during bus clock cycle 5.

[0032] Referring now to FIG. 6, a diagram of a break event handler is shown, according to one embodiment of the present disclosure. In one embodiment, the processor clock grid may be powered down during an enhanced low-power state. External pins of processor 210 may characterize break events from the enhanced low-power state that cause the enhanced low-power state to transfer (“break”) away to another state. In some embodiments, these break event pins may include STPCLK de-assertion, reset assertion, interrupt assertion, non-maskable interrupt (NMI) assertion, system management interrupt (SMI) assertion, or machine check assertion. In other embodiments, other external break events may be used. A break event monitor 620 may be used in processor 210 to determine these break events. If one is detected, then break event monitor 620 may signal trigger enhanced low-power state transition logic 610 to change value in the goal frequency and voltage register 422 of FIG. 4. The trigger enhanced low-power state transition logic 610 operates under the status provided by enhanced low-power state status logic 612. Break event monitor 620 may also signal clock grid control 640 to power up the clock distribution grid.

[0033] Similarly, snoop pins may include bus priority (BPRI) signal pins and other pins related to cache-coherency snooping. If a snoop request is detected, then snoop monitor 630 may not signal trigger enhanced low-power state transition logic 610 to change value in the goal frequency and voltage register 422 of FIG. 4. Snoop monitor 630 will signal clock grid control 640 to power up the clock distribution grid, in order to service the snoop request.

[0034] Referring now to FIG. 7, a schematic diagram of a microprocessor system is shown, according to one embodiment of the present disclosure. The FIG. 7 system may include several processors of which only two, processors 40, 60 are shown for clarity. Processors 40, 60 may be the processor 210 of FIG. 2. Processors 40, 60 may include caches 42, 62. The FIG. 7 multiprocessor system may have several functions connected via bus interfaces 44, 64, 12, 8 with a system bus 6. In one embodiment, system bus 6 may be the front side bus (FSB) utilized with Pentium® class microprocessors manufactured by Intel® Corporation. A general name for a function connected via a bus interface with a system bus is an “agent”. Examples of agents are processors 40, 60, bus bridge 32, and memory controller 34. In some embodiments memory controller 34 and bus bridge 32 may collectively be referred to as a chipset, and may be the chipset 220 of FIG. 2. In some embodiments, functions of a chipset may be divided among physical chips differently than as shown in the FIG. 7 embodiment.

[0035] Memory controller 34 may permit processors 40, 60 to read and write from system memory 10 and from a basic input/output system (BIOS) erasable programmable read-only memory (EPROM) 36. In some embodiments BIOS EPROM 36 may utilize flash memory. Memory controller 34 may include a bus interface 8 to permit memory read and write data to be carried to and from bus agents on system bus 6. Memory controller 34 may also connect with a high-performance graphics circuit 38 across a high-performance graphics interface 39. In certain embodiments the high-performance graphics interface 39 may be an advanced graphics port AGP interface, or an AGP interface operating at multiple speeds such as 4X AGP or 8X AGP. Memory controller 34 may direct read data from system memory 10 to the high-performance graphics circuit 38 across high-performance graphics interface 39.

[0036] Bus bridge 32 may permit data exchanges between system bus 6 and bus 16, which may in some embodiments be a industry standard architecture (ISA) bus or a peripheral component interconnect (PCI) bus. There may be various input/output I/O devices 14 on the bus 16, including in some embodiments low performance graphics controllers, video controllers, and networking controllers. Another bus bridge 18 may in some embodiments be used to permit data exchanges between bus 16 and bus 20. Bus 20 may in some embodiments be a small computer system interface (SCSI) bus, an integrated drive electronics (IDE) bus, or a universal serial bus (USB) bus. Additional I/O devices may be connected with bus 20. These may include keyboard and cursor control devices 22, including mice, audio I/O 24, communications devices 26, including modems and network interfaces, and data storage devices 28. Software code 30 may be stored on data storage device 28. In some embodiments, data storage device 28 may be a fixed magnetic disk, a floppy disk drive, an optical disk drive, a magneto-optical disk drive, a magnetic tape, or non-volatile memory including flash memory.

[0037] In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 

What is claimed is:
 1. An apparatus, comprising: a processor to operate in a normal operation state and a low-power state; and an enhanced state policy logic to initiate a transfer from said low-power state to an enhanced low-power state.
 2. The apparatus of claim 1, wherein transfer includes changing a first supply voltage to a second supply voltage.
 3. The apparatus of claim 2, wherein said second supply voltage supports said processor at a reduced frequency.
 4. The apparatus of claim 2, wherein said transfer includes changing a first clock frequency to a second clock frequency.
 5. The apparatus of claim 2, wherein said second supply voltage is set by said processor issuing a voltage identification code.
 6. The apparatus of claim 2, wherein said transfer includes turning a clock grid off.
 7. The apparatus of claim 6, wherein said clock grid does not include a processor bus interface domain.
 8. The apparatus of claim 1, wherein said enhanced state policy logic is to break from said enhanced low-power state to said normal operation state by a break event from said low-power state.
 9. The apparatus of claim 1, wherein said enhanced state policy logic is to break from said enhanced low-power state to an enhanced snoop state, wherein said enhanced snoop state operates at a lower voltage and frequency than said normal operation state.
 10. The apparatus of claim 1, wherein said low-power state is a halt state.
 11. A method, comprising: transferring a processor from a normal operation state to a low-power state; and generating internally to said processor a transfer from said low-power state to an enhanced low-power state.
 12. The method of claim 11, wherein said generating includes powering-down a clock grid.
 13. The method of claim 12, wherein said generating includes setting a ratio of bus clock frequency to processor core clock frequency.
 14. The method of claim 13, wherein said generating includes setting a voltage compatible with said ratio.
 15. The method of claim 14, wherein said powering-down does not include powering-down a processor bus interface domain.
 16. The method of claim 15, further comprising responding to a snoop request using circuits of said processor bus interface domain.
 17. The method of claim 14, further comprising powering-on said clock grid and responding to a snoop request.
 18. An apparatus, comprising: means for transferring a processor from a normal operation state to a low-power state; and means for generating internally to said processor a transfer from said low-power state to an enhanced low-power state.
 19. The apparatus of claim 18, wherein said means for generating includes means for powering-down a clock grid.
 20. The apparatus of claim 19, wherein said means for generating includes means for setting a ratio of bus clock frequency to processor core clock frequency.
 21. The apparatus of claim 20, wherein said means for generating includes means for setting a voltage compatible with said ratio.
 22. The apparatus of claim 21, wherein said means for powering-down do not power-down a processor bus interface domain.
 23. The apparatus of claim 22, further comprising means for responding to a snoop request using circuits of said processor bus interface domain.
 24. The apparatus of claim 21, further comprising means for powering-on said clock grid and means for responding to a snoop request.
 25. A system, comprising: a processor to operate in a normal operation state and a low-power state; an enhanced state policy logic to initiate a transfer from said low-power state to an enhanced low-power state; a voltage regulation module to receive said transfer; and a chipset to issue a stop clock signal to said processor.
 26. The system of claim 25, wherein transfer includes changing a first supply voltage to a second supply voltage.
 27. The system of claim 26, wherein said second supply voltage supports said processor at a reduced frequency.
 28. The system of claim 27, wherein said second supply voltage is set by said processor issuing a voltage identification code to said voltage regulation module.
 29. The system of claim 26, wherein said transfer includes turning a clock grid off.
 30. The system of claim 29, wherein said clock grid does not include a processor bus interface domain. 